The present invention relates to latching devices and in particular to a device for latching a circuit board module to its mounting rack.
Complex and large electric circuit networks such as systems control networks for ships or nuclear reactors are typically broken down into a plurality of small circuits each mounted on a modular circuit board. The circuit boards, which are electrically interconnected to make up the network, enable fast and easy replacement of failed circuit parts as well as greater flexibility of design.
Circuit boards are typically rectangular and mounted vertically in racks. Generally, the top and bottom edges of the boards slide in tracks and the back edge is equipped with some electrical connector means.
The front of the circuit board module is equipped with a plate for handling, identification and asthetic purposes. Also some mechanism is typically provided to lock the circuit board module to the circuit board rack. This is desired to prevent withdrawal of the module and thereby breaking of the circuit network in the event of some withdrawal force being applied to the circuit board by accident, e.g., earthquakes, vibrations, sudden ship reeling movements or jarring by the end of a janitor's mop handle. The present invention is such a latching mechanism.
One known prior art latching mechanism is the screw type. A machined screw extends through the front plate of the module and threadingly engages a threaded hole on the rack. The shortcomings of the screw type include the necessity of manufacturing, stocking and assembling costly machined parts and the need to employ a separate tool to assure a positive and lasting engagement.
Another known prior art latching mechanism is the plunger type wherein a plunger is slidably disposed in an expandable sleeve attached to the front plate. Upon insertion of the modular circuit board into the rack, the sleeve penetrates a hole provided therefor. Once so positioned, forcing the plunger through the sleeve expands the sleeve to a dimension greater than that of the hole and thereby effecting a latch, to preclude withdrawal of the sleeve through the hole. The shortcomings of the plunger type include stocking and assembly costs, the fact that currently there is but a single source of supply for this particular device and the ability to completely insert the circuit board module into working position in the rack without actually effecting the latch.